Coronary heart disease (CHD) has become the leading cause of death among women beyond age 60. Knowledge about lipid- lowering or other interventions that may be useful in preventing progression or causing regression of coronary artery atherosclerosis among postmenopausal women is essentially nonexistent. Randomized trails of the effect of plasma cholesterol lowering on CHD have not included women. Observational epidemiologic studies examining the association between estrogen use and CHD in postmenopausal women have reported contradictory results. The significance of this proposed study is that it will provide a foundation for trials in women and may provide a basis for the rational management of hyperlipoproteinemic postmenopausal women. The results of this study will have significance in several areas: a) the study will determine whether and to what extent estrogen replacement decreases coronary artery atherosclerosis among estrogen-deficient postmenopausal monkeys on a cholesterol lowering diet; b) the results will allow us to determine whether and to what extent the addition of a progestin (Provera) to the estrogen replacement therapy will diminish any beneficial effect of estrogen replacement therapy; in subgroup analyses based on the prerandomization data, two additional questions will be answered: c) What is the effect of hormonal therapy on the HDL subclasses and the LDL molecular weight, all known to be associated with atherosclerotic lesions? and finally, d) What is the relationship between the plasma levels of sex hormone binding globulin and the degree of coronary atherosclerosis? The study represents the first effort that we are aware of to utilize the methodology of a randomized trial in a nonhuman primate population to evaluate a coronary atherosclerosis intervention. Moreover, it is a complement to the NIH-sponsored PEPI (Postmenopausal Estrogen/Progestin Interventions) study which is designed to determine the effect of different estrogen/progestin preparations on CHD and osteoporosis risk factors and other factors, as well as their safety.